150 SEXUAL DIMORPHISM 



This is, therefore, one of the numerous cases in which the 

 special development of plumage is limited not merely to one 

 sex, but to the season of the year during which the male 

 practises certain violent movements and gestures under the 

 influence of sexual excitement. 



The published observations prove that the habits of male 

 and female in relation to breeding are as different as their 

 plumage. The female alone performs the duty of incubation 

 and probably builds her nest without aid from the male. The 

 nest is roofed over and has an aperture only at one end. It 

 has been considered strange that so large a bird with so long 

 a tail should sit in a roofed, enclosed nest, but it has been 

 observed by Mr. Ramsay that she enters the nest head first 

 and then turns round, bending the tail over her back or to 

 the side. We may infer therefore that the length of tail 

 in the female is due to partial inheritance from the male, and 

 not to any special stimulation involved in her own habits. 1 



Ploceidce. Among the Ploceidse or Weavers the Widow-bird 

 of South and West Africa is remarkable for the extremely long 

 tail-feathers of the male. These are present only in the breed- 

 ing season, and in winter plumage the male is scarcely different 

 from the female. Darwin mentions a statement that the 

 female rejected the male when he was deprived of his long 

 tail feathers, and considers the observation as evidence of the 

 occurrence of selection. But it would rather tend to show 

 that in the female the sexual instinct was associated with 

 the perception of the special male adornment, an association 

 which probably exists in all such cases. The growth of these 

 feathers, taking place every year at the approach of the 

 breeding season, like the growth of the antlers of stags, must, 

 I believe, be due to some special stimulation of the feather- 

 papillae produced by movements associated with the instincts 



1 See Gould, Handbook to the Birds of Australia, 1865, vol. i. Ramsay, 

 Proc. Zool. Soc., 1868. T. W. Wood, The Student, April, 1870. 



